Location Determination

ABSTRACT

Systems, methods, and computer program products obtain power information indicating a detected power of respective signals received in a mobile device from multiple transmitters. Using at least the obtained power information, respective probability values for a plurality of positions are determined, each probability value indicating a probability that the mobile device is in a corresponding position. An estimated position of the mobile device is identified based at least in part on the determined probability values.

BACKGROUND

This specification is related generally to location determination.

The increased importance of processor-based devices has made navigation services and other forms of location determination available to a substantial number of users. For example, online services are now available that can provide maps, directions, navigation information and other information relating to the geography of places on Earth and also in the sky.

Some devices are intended for portable use and are therefore sometimes referred to as mobile. Some of them rely on a form of radio communication to connect to a home station, a network or some other base, with which information can be exchanged. With some mobile devices the range of radio signal coverage is substantial and the users can therefore operate the device anywhere in a significant geographic area. This ability to move around with the device also increases the need to determine the location of the device, to a more or less exact geographic position. Some technologies have been introduced in this regard, including Global Positioning System (GPS) and other approaches that use signals from transmitters on the ground.

SUMMARY

The present invention relates to location determination of a mobile device. A statistical model is built based on the measured power levels (e.g., signal strength) of signals received by a mobile device from one or more transmitters and their respective locations. Other information, such as the last known or estimated location of the mobile device, and/or geographical information, can also be used to build the statistical model. The statistical model is then used to determine the likelihood that the mobile device is located at one or more randomly or pseudo randomly selected positions within a region surrounding a last known location of the mobile device, or a region surrounding a reference point (e.g., a cellular transmission tower) near the mobile device. The probability that the mobile device is at the selected positions is used to estimate the location of the mobile device.

In a first aspect, one method includes the actions of obtaining power information indicating a detected power of respective signals received in a mobile device from multiple transmitters, determining, using at least the obtained power information, respective probability values for a plurality of positions, each probability value indicating a probability that the mobile device is in a corresponding position, and identifying an estimated position of the mobile device based at least in part on the determined probability values.

Implementations can include any, all or none of the following features. Determining the probability values and identifying the estimated position can include generating a statistical model based at least in part on the obtained power information, selecting a geographical region to which the generated statistical model applies, and randomly or pseudo randomly selecting a plurality of positions within the selected geographical region, where each of the probability values is identified as being associated with a corresponding one of the plurality of positions. According to another feature, the method can also include determining that a previous location of the mobile device has been registered, where the geographical region is selected taking into account the registered previous location.

According to yet another feature, the method includes the actions of determining a first transmitter, among the multiple transmitters, having a strongest signal according to the obtained power information, where the geographical region is selected taking into account a location of the determined first transmitter. According to still another feature, where multiple previous location determinations have been performed, the method can include generating an error estimate for a most recent of the previous location determinations, where the geographical region is selected taking into account the generated error estimate.

In another feature, the statistical model is configured to have at least one term added and be taken into account in determining the probability values. Additionally, for each of the multiple transmitters, a term can be added to the statistical model, the term reflecting that a conditional probability that the mobile device is a distance d from the respective transmitter follows a log-normal distribution, where a mean and a standard deviation of the log-normal distribution are functions of the power of the respective transmitter. According to another feature, the method includes obtaining a training data set that includes signal strength information regarding known locations, and estimating the functions for the mean and the standard deviation using the obtained training data set.

According to a feature, for each pair of the multiple transmitters, a term can be added to the statistical model, the term reflecting that a conditional probability that the mobile device is at a distance d from a point on a line joining the pair of the multiple transmitters follows a log-normal distribution, where a mean and a standard deviation are functions of the powers of the respective two transmitters. According to yet another feature, the method can include the actions of obtaining a training data set comprising signal strength information regarding known locations, and estimating the functions for the mean and the standard deviation using the obtained training data set.

In another feature the method can include the actions of obtaining a previously estimated location for the mobile device, and adding a term to the statistical model, the term reflecting that a conditional probability that the mobile device is at a distance d from the previously estimated location follows a radially symmetric Gaussian distribution about the previously estimated location. The standard deviation of the radially symmetric Gaussian distribution can be based on an error estimate and on information about how recently the previously estimated location was identified.

According to still another feature, the method can include the actions of obtaining geographical information relating to at least one of the plurality of positions, and adding a term to the statistical model based on the obtained geographical information. The geographical information can provide a bias toward some locations over other locations. Further, identifying the estimated position can include the actions of selecting one of the determined probability values that is associated with a highest probability that the mobile device is in the corresponding position, and/or determining a centroid location based on the determined probability values, and selecting the determined centroid location as the estimated position.

According to yet another feature, the method can include determining that additional power information is required to identify the estimated position, postponing the identification of the estimated position for a period of time, and collecting the additional power information, wherein the estimated position of the mobile device is identified based also on the additional power information.

These general and specific aspects may be implemented using a system, a method, or a computer program, or any combination of systems, methods, and computer programs.

Particular embodiments of the subject matter described in this specification can be implemented to realize none, one or more of the following advantages. Improved location determination can be provided.

The details of one or more embodiments of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example mobile device.

FIG. 2 is a block diagram of an example network operating environment for the mobile device of FIG. 1.

FIG. 3 is a block diagram of an example implementation of the mobile device of FIG. 1.

FIG. 4 shows a schematic illustration of a mobile device and four exemplary transmitters.

FIG. 5 shows the signal and/or location information used to generate a statistical model.

FIG. 6A is a flow chart of an example first process of determining the contribution to the statistical model based on the measured power levels from one or more transmitters and the location of the one or more transmitters.

FIG. 6B is a flow chart of an example second process of determining the contribution to the statistical model based on the measured power levels from one or more transmitters and the location of the one or more transmitters.

FIG. 7 shows an example of a process to estimate the location of a mobile device.

FIG. 8 shows an illustrative map display on an example mobile device.

Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an example mobile device 100. The mobile device 100 can be, for example, a handheld computer, a personal digital assistant, a cellular telephone, a network appliance, a camera, a smart phone, an enhanced general packet radio service (EGPRS) mobile phone, a network base station, a media player, a navigation device, an email device, a game console, or a combination of any two or more of these data processing devices or other data processing devices. Below will be described examples of determining the location of a device such as the mobile device 100. For example, the location can be determined using a statistical model that takes into account at least received signal strength.

In some implementations, the mobile device 100 includes a touch-sensitive display 102. The touch-sensitive display 102 can implement liquid crystal display (LCD) technology, light emitting polymer display (LPD) technology, or some other display technology. The touch sensitive display 102 can be sensitive to haptic and/or tactile contact with a user.

In some implementations, the touch-sensitive display 102 can comprise a multi-touch-sensitive display 102. A multi-touch-sensitive display 102 can, for example, process multiple simultaneous touch points, including processing data related to the pressure, degree, and/or position of each touch point. Such processing facilitates gestures and interactions with multiple fingers, chording, and other interactions. Other touch-sensitive display technologies can also be used, e.g., a display in which contact is made using a stylus or other pointing device. Some examples of multi-touch-sensitive display technology are described in U.S. Pat. Nos. 6,323,846, 6,570,557, 6,677,932, and 6,888,536, each of which is incorporated by reference herein in its entirety.

In some implementations, the mobile device 100 can display one or more graphical user interfaces on the touch-sensitive display 102 for providing the user access to various system objects and for conveying information to the user. In some implementations, the graphical user interface can include one or more display objects 104, 106. In the example shown, the display objects 104, 106, are graphic representations of system objects. Some examples of system objects include device functions, applications, windows, files, alerts, events, or other identifiable system objects.

In some implementations, the mobile device 100 can implement multiple device functionalities, such as a telephony device, an e-mail device, a network data communication device, a Wi-Fi base station device (not shown), and a media processing device. In some implementations, particular display objects 104 can be displayed in a menu bar 118. In some implementations, device functionalities can be accessed from a top-level graphical user interface, such as the graphical user interface illustrated in FIG. 1. Touching one of the objects 104 can, for example, invoke corresponding functionality.

In some implementations, the mobile device 100 can implement network distribution functionality. For example, the functionality can enable the user to take the mobile device 100 and provide access to its associated network while traveling. In particular, the mobile device 100 can extend Internet access (e.g., Wi-Fi) to other wireless devices in the vicinity. For example, mobile device 100 can be configured as a base station for one or more devices. As such, mobile device 100 can grant or deny network access to other wireless devices.

In some implementations, upon invocation of device functionality, the graphical user interface of the mobile device 100 changes, or is augmented or replaced with another user interface or user interface elements, to facilitate user access to particular functions associated with the corresponding device functionality. For example, in response to a user touching a phone object, the graphical user interface of the touch-sensitive display 102 may present display objects related to various phone functions; likewise, touching of an email object may cause the graphical user interface to present display objects related to various e-mail functions; touching a Web object may cause the graphical user interface to present display objects related to various Web-surfing functions; and touching a media player object may cause the graphical user interface to present display objects related to various media processing functions.

In some implementations, the top-level graphical user interface environment or state of FIG. 1 can be restored by pressing a button 120 located near the bottom of the mobile device 100. In some implementations, each corresponding device functionality may have corresponding “home” display objects displayed on the touch-sensitive display 102, and the graphical user interface environment of FIG. 1 can be restored by pressing the “home” display object.

In some implementations, the top-level graphical user interface can include additional display objects 106, such as a short messaging service (SMS) object, a calendar object, a photos object, a camera object, a calculator object, a stocks object, a weather object, a maps object 144, a notes object, a clock object, an address book object, and a settings object. Touching the maps object 144 can, for example, invoke a mapping and location-based services environment and supporting functionality; likewise, a selection of any of the display objects 106 can invoke a corresponding object environment and functionality.

Additional and/or different display objects can also be displayed in the graphical user interface of FIG. 1. For example, if the device 100 is functioning as a base station for other devices, one or more “connection” objects may appear in the graphical user interface to indicate the connection. In some implementations, the display objects 106 can be configured by a user, e.g., a user may specify which display objects 106 are displayed, and/or may download additional applications or other software that provides other functionalities and corresponding display objects.

In some implementations, the mobile device 100 can include one or more input/output (I/O) devices and/or sensor devices. For example, a speaker 160 and a microphone 162 can be included to facilitate voice-enabled functionalities, such as phone and voice mail functions. In some implementations, an up/down button 184 for volume control of the speaker 160 and the microphone 162 can be included. The mobile device 100 can also include an on/off button 182 for a ring indicator of incoming phone calls. In some implementations, a loud speaker 164 can be included to facilitate hands-free voice functionalities, such as speaker phone functions. An audio jack 166 can also be included for use of headphones and/or a microphone.

In some implementations, a proximity sensor 168 can be included to facilitate the detection of the user positioning the mobile device 100 proximate to the user's ear and, in response, to disengage the touch-sensitive display 102 to prevent accidental function invocations. In some implementations, the touch-sensitive display 102 can be turned off to conserve additional power when the mobile device 100 is proximate to the user's ear.

Other sensors can also be used. For example, in some implementations, an ambient light sensor 170 can be utilized to facilitate adjusting the brightness of the touch-sensitive display 102. In some implementations, an accelerometer 172 can be utilized to detect movement of the mobile device 100, as indicated by the directional arrow 174. Accordingly, display objects and/or media can be presented according to a detected orientation, e.g., portrait or landscape. In some implementations, the mobile device 100 may include circuitry and sensors for supporting a location determining capability, such as that provided by the Global Positioning System (GPS) or other positioning systems (e.g., systems using Wi-Fi access points, television signals, cellular grids, Uniform Resource Locators (URLs)). In some implementations, a positioning system (e.g., a GPS receiver) can be integrated into the mobile device 100 or provided as a separate device that can be coupled to the mobile device 100 through an interface (e.g., port device 190) to provide access to location-based services.

In some implementations, a port device 190, e.g., a Universal Serial Bus (USB) port, or a docking port, or some other wired port connection, can be included. The port device 190 can, for example, be utilized to establish a wired connection to other computing devices, such as other communication devices 100, network access devices, a personal computer, a printer, a display screen, or other processing devices capable of receiving and/or transmitting data. In some implementations, the port device 190 allows the mobile device 100 to synchronize with a host device using one or more protocols, such as, for example, the TCP/IP, HTTP, UDP and any other known protocol.

The mobile device 100 can also include a camera lens and sensor 180. In some implementations, the camera lens and sensor 180 can be located on the back surface of the mobile device 100. The camera can capture still images and/or video.

The mobile device 100 can also include one or more wireless communication subsystems, such as an 802.11b/g communication device 186, and/or a Bluetooth™ communication device 188. Other communication protocols can also be supported, including other 802.x communication protocols (e.g., WiMax, Wi-Fi, 3G), code division multiple access (CDMA), global system for mobile communications (GSM), Enhanced Data GSM Environment (EDGE), etc.

FIG. 2 is a block diagram of an example network operating environment 200. In FIG. 2, mobile devices 202 a and 202 b each can represent mobile device 100. Mobile devices 202 a and 202 b can, for example, communicate over one or more wired and/or wireless networks 210 in data communication. For example, a wireless network 212, e.g., a cellular network, can communicate with a wide area network (WAN) 214, such as the Internet, by use of a gateway 216. Likewise, an access device 218, such as an 802.11g wireless access device, can provide communication access to the wide area network 214. In some implementations, both voice and data communications can be established over the wireless network 212 and the access device 218. For example, the mobile device 202 a can place and receive phone calls (e.g., using VoIP protocols), send and receive e-mail messages (e.g., using POP3 protocol), and retrieve electronic documents and/or streams, such as web pages, photographs, and videos, over the wireless network 212, gateway 216, and wide area network 214 (e.g., using TCP/IP or UDP protocols). Likewise, in some implementations, the mobile device 202 b can place and receive phone calls, send and receive e-mail messages, and retrieve electronic documents over the access device 218 and the wide area network 214. In some implementations, the mobile device 202 a or 202 b can be physically connected to the access device 218 using one or more cables and the access device 218 can be a personal computer. In this configuration, the mobile device 202 a or 202 b can be referred to as a “tethered” device.

The mobile devices 202 a and 202 b can also establish communications by other means. For example, the wireless device 202 a can communicate with other wireless devices, e.g., other mobile devices 202 a or 202 b, cell phones, etc., over the wireless network 212. Likewise, the mobile devices 202 a and 202 b can establish peer-to-peer communications 220, e.g., a personal area network, by use of one or more communication subsystems, such as the Bluetooth™ communication devices 188 shown in FIG. 1. Other communication protocols and topologies can also be implemented.

The mobile device 202 a or 202 b can, for example, communicate with one or more services 230, 240, 250, 260, and 270 over the one or more wired and/or wireless networks 210. For example, one or more navigation services 230 can provide navigation information, e.g., map information, location information, route information, and other information, to the mobile device 202 a or 202 b. A user of the mobile device 202 b can invoke a map functionality, e.g., by pressing the maps object 144 on the top-level graphical user interface shown in FIG. 1, and can request and receive a map for a particular location, request and receive route directions, or request and receive listings of businesses in the vicinity of a particular location, for example. In other implementations, location determination can be performed locally on the mobile device 202 a or 202 b. For example, the navigation service 230 can be implemented on the mobile device 202 a or 202 b.

A messaging service 240 can, for example, provide e-mail and/or other messaging services. A media service 250 can, for example, provide access to media files, such as song files, audio books, movie files, video clips, and other media data. In some implementations, separate audio and video services (not shown) can provide access to the respective types of media files. A syncing service 260 can, for example, perform syncing services (e.g., sync files). An activation service 270 can, for example, perform an activation process for activating the mobile device 202 a or 202 b. Other services can also be provided, including a software update service that automatically determines whether software updates exist for software on the mobile device 202 a or 202 b, then downloads the software updates to the mobile device 202 a or 202 b where the software updates can be manually or automatically unpacked and/or installed.

The mobile device 202 a or 202 b can also access other data and content over the one or more wired and/or wireless networks 210. For example, content publishers, such as news sites, RSS feeds, web sites, blogs, social networking sites, developer networks, etc., can be accessed by the mobile device 202 a or 202 b. Such access can be provided by invocation of a web browsing function or application (e.g., a browser) in response to a user touching, for example, a Web object.

FIG. 3 is a block diagram 300 of an example implementation of the mobile device 100 of FIG. 1. The mobile device 100 can include a memory interface 302, one or more data processors, image processors and/or central processing units 304, and a peripherals interface 306. The memory interface 302, the one or more processors 304 and/or the peripherals interface 306 can be separate components or can be integrated in one or more integrated circuits. The various components in the mobile device 100 can be coupled by one or more communication buses or signal lines.

Sensors, devices, and subsystems can be coupled to the peripherals interface 306 to facilitate multiple functionalities. For example, a motion sensor 310, a light sensor 312, and a proximity sensor 314 can be coupled to the peripherals interface 306 to facilitate the orientation, lighting, and proximity functions described with respect to FIG. 1. Other sensors 316 can also be connected to the peripherals interface 306, such as a positioning system (e.g., GPS receiver), a temperature sensor, a biometric sensor, or other sensing device, to facilitate related functionalities.

A camera subsystem 320 and an optical sensor 322, e.g., a charged coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) optical sensor, can be utilized to facilitate camera functions, such as recording photographs and video clips.

Communication functions can be facilitated through one or more wireless communication subsystems 324, which can include radio frequency receivers and transmitters and/or optical (e.g., infrared) receivers and transmitters. The specific design and implementation of the communication subsystem 324 can depend on the communication network(s) over which the mobile device 100 is intended to operate. For example, a mobile device 100 may include communication subsystems 324 designed to operate over a GSM network, a GPRS network, an EDGE network, a Wi-Fi or WiMax network, and a Bluetooth™ network. In particular, the wireless communication subsystems 324 may include hosting protocols such that the device 100 may be configured as a base station for other wireless devices. In some implementations, a strength of signals received using any or all of the communication subsystems 324 can be determined; power information indicating such strength can be obtained and used in estimating a location of the mobile device 100.

An audio subsystem 326 can be coupled to a speaker 328 and a microphone 330 to facilitate voice-enabled functions, such as voice recognition, voice replication, digital recording, and telephony functions.

The I/O subsystem 340 can include a touch screen controller 342 and/or other input controller(s) 344. The touch-screen controller 342 can be coupled to a touch screen 346. The touch screen 346 and touch screen controller 342 can, for example, detect that contact and/or movement begins or ends using any of a plurality of touch sensitivity technologies, including but not limited to capacitive, resistive, infrared, and surface acoustic wave technologies, as well as other proximity sensor arrays or other elements for determining one or more points of contact with the touch screen 346.

The other input controller(s) 344 can be coupled to other input/control devices 348, such as one or more buttons, rocker switches, thumb-wheel, infrared port, USB port, and/or a pointer device such as a stylus. The one or more buttons (not shown) can include an up/down button for volume control of the speaker 328 and/or the microphone 330.

In one implementation, a pressing of the button for a first duration may disengage a lock of the touch screen 346; and a pressing of the button for a second duration that is longer than the first duration may turn power to the mobile device 100 on or off. The user may be able to customize a functionality of one or more of the buttons. The touch screen 346 can, for example, also be used to implement virtual or soft buttons and/or a keyboard.

In some implementations, the mobile device 100 can present recorded audio and/or video files, such as MP3, AAC, and MPEG files. In some implementations, the mobile device 100 can include the functionality of an MP3 player, such as an iPod™. The mobile device 100 may, therefore, include a 36-pin connector that is compatible with the iPod. Other input/output and control devices can also be used.

The memory interface 302 can be coupled to memory 350. The memory 350 can include high-speed random access memory and/or non-volatile memory, such as one or more magnetic disk storage devices, one or more optical storage devices, and/or flash memory (e.g., NAND, NOR). The memory 350 can store an operating system 352, such as Darwin, RTXC, LINUX, UNIX, OS X, WINDOWS, or an embedded operating system such as VxWorks. The operating system 352 may include instructions for handling basic system services and for performing hardware dependent tasks. In some implementations, the operating system 352 can be a kernel (e.g., UNIX kernel).

The memory 350 may also store communication instructions 354 to facilitate communicating with one or more additional devices, one or more computers and/or one or more servers. The memory 350 may include graphical user interface instructions 356 to facilitate graphic user interface processing; sensor processing instructions 358 to facilitate sensor-related processing and functions; phone instructions 360 to facilitate phone-related processes and functions; electronic messaging instructions 362 to facilitate electronic-messaging related processes and functions; web browsing instructions 364 to facilitate web browsing-related processes and functions; media processing instructions 366 to facilitate media processing-related processes and functions; GPS/Navigation instructions 368 to facilitate GPS and navigation-related processes and instructions; camera instructions 370 to facilitate camera-related processes and functions; and/or other software instructions 372 to facilitate other processes and functions, e.g., security processes and functions. In some implementations, some or all of the instruction 368 can be executed to cause a location of the mobile device 100 to be determined, for example by selecting a location determination technique to be used. The instructions 358 can be configured so that also one or more, or all, of the other instructions in the memory 350 can be used in performing a function. The memory 350 may also store other software instructions (not shown), such as web video instructions to facilitate web video-related processes and functions; and/or web shopping instructions to facilitate web shopping-related processes and functions. In some implementations, the media processing instructions 366 are divided into audio processing instructions and video processing instructions to facilitate audio processing-related processes and functions and video processing-related processes and functions, respectively. An activation record and International Mobile Equipment Identity (IMEI) 374 or similar hardware identifier can also be stored in memory 350.

Each of the above identified instructions and applications can correspond to a set of instructions for performing one or more functions described above. These instructions need not be implemented as separate software programs, procedures, or modules. The memory 350 can include additional instructions or fewer instructions. Furthermore, various functions of the mobile device 100 may be implemented in hardware and/or in software, including in one or more signal processing and/or application specific integrated circuits.

FIG. 4 shows a schematic illustration of four exemplary transmitters 400-1 through 400-4 and a mobile device 402. Here, the mobile device 402 can represent a mobile device such as the mobile devices described above with respect to FIGS. 1-3. The mobile device 402 can communicate with one or more of the transmitters 400 which can include network access points, e.g., Wi-Fi base station devices, or a cell tower, or a remote transmitter such as a satellite, to name a few examples. In some implementations, access points can be any combination of 802.11b/g wireless routers, 802.11n wireless routers, and some other Wi-Fi devices that implement any suitable Wi-Fi or other wireless networking technology or protocol.

Using the communication with the access points and/or the cell towers, a position estimator 404 can estimate the geographic area and/or location where the mobile device 402 is currently located. The estimation can be based at least in part on signal and/or location information 406, including the signal strengths of the respective transmitters 400-1 through 400-4. In this example the information 406 can be located on the mobile device 402. In other implementations, the position estimator 404 and/or the signal and/or location information 406 can be maintained elsewhere than on the mobile device 402, such as on a server device in communication with the mobile device.

The mobile device 402 can, for example, receive a signal from the transmitter 400-1. The signal can include an identifier for the transmitter 400-1 and in some implementations can include other information, such as the latitude and longitude of the transmitter 400-1. In some implementations, the latitude and longitude of the transmitter can be determined on the device 402 or remotely at a server using a database. The position estimator 406 can, for example, with a degree of uncertainty or error, identify an estimated position of the mobile device 402 using the information 406.

In some implementations, the accuracy or precision of the estimated position is stated in units of distance (e.g., “the estimated position is accurate up to 50 meters”). That is, the actual position of the mobile device 402 can be within the accuracy distance from the estimated position. For example, a first geographic area can be a circle centered at the latitude and longitude of the estimated position with a radius equal to the stated accuracy or precision (e.g., 38 meters if the accuracy of the estimated position is up to 38 meters). The first geographic area can alternatively be represented on a map display as a square, rectangle, oval, diamond, triangle, or some other shaped enclosed region.

The mobile device 402 can, for example, connect to additional devices or services (not shown) for location-based services, instead of, or in addition to the transmitter(s) 400. Such devices or services could include a Bluetooth™ device, GPS, radio or TV towers, or cellular grids, to name a few examples. For example, the mobile device 402 can connect to peer devices with the Bluetooth™ communication device 188 (FIG. 1) and receive location-based information from other mobile devices and/or Bluetooth™ enabled devices. In some implementations, the mobile device 402 can determine or estimate its position and/or geographic area using other technologies (e.g., GPS).

In some implementations, position estimates are generated using a statistical model, for instance, by the position estimator 404. Such a model can be based at least in part on power information regarding one or more transmitters. The model can be used to generate a distribution of one or more position samples that are used to estimate the current location of the mobile device as explained in greater detail below.

A. Statistical Model Components

FIG. 5 shows the signal and/or location information 406 that can be used to generate a statistical model 530 that is used to estimate the location of a mobile device, such as mobile device 406. According to some implementations, the statistical model 530 is generated by the position estimator 404. As described with respect to FIG. 4, the measured power levels (i.e., signal strength) of signals received by the device from one or more transmitters 505 and the location of known transmitters 510 are used to generate the statistical model 530.

For instance, the mobile device 402 can obtain received signal strength indicators (RSSIs) and a unique ID associated with each signal from a transmitter. The geographical location of the transmitter (e.g., a cell tower) can be looked up using the transmitter ID, either by querying a remote server or by a lookup process in a database stored on the mobile device. If a cell tower contains several transmitters, their RSSIs can be combined to a single RSSI for the cell tower, for example by taking a maximum of the received signals from the transmitters at issue.

In some implementations, a transformation can be applied to coordinates of the transmitters. For example, latitude-longitude pairs can be transformed into values representing relative transmitter location, such as with regard to a transmitter having the strongest signal. That is, in some implementations a latitude-longitude pair can be transformed to meters North and meters East from the transmitter with the strongest signal.

Referring again to FIG. 5, other information can optionally be used to generate the statistical model 530. This includes historical position information 515 and/or geographical information 520.

Historical position information 515 can be used to generate and/or modify the statistical model 530, for instance, by the position estimator 404. Historical position information 515 (which includes recently known location information) can be based on previous estimate locations, for instance, as determined by the position estimator 404, and/or based on position information obtained from other data sources in communication with the device 402. For instance, historical position information 515 can be obtained from wifi hotspots or from other devices, such as GPS units, that can perform location estimation. Historical position information 515 can contribute to the statistical model so that the model can account for last known positions of the device 402. As explained in greater detail below with respect to FIG. 6, recent known locations of the device 402 are presumed to be more accurate than old measurements, and thus how recent the position information factors into the statistical model.

Geographical information 520 can also be used to focus a probability determination to location points that are more likely locations for the mobile device than another location. This information provides a bias to locations that the device is more likely to be near. For instance, locations such as a highway or a populated area, such as a shopping mall, may be biased over locations that the device 402 is less likely to be near, such as in the middle of city blocks, in the middle of a lake, on a service road, etc.

B. Signal Strength and Transmitter Locations Contribution to a Statistical Model

FIG. 6A shows a first process 600 of determining the contribution to the statistical model 530 based on the measured power levels (e.g., signal strength) of signals received by the device from one or more transmitters 505 and the location of known transmitters 510. Each source (e.g., tower) from which a signal is received by the device is identified 605. A term is added to the statistical model for each source 620 based on the identified location of each source 610 and the identified signal strength received from each source 615. In some implementations, the term added to the statistical model for each source is based on an assumption that the conditional probability that the device is located at a distance d from a source follows a log-normal distribution having mean and standard deviations that are functions of the signal strength associated with the source.

According to some implementations, a training set of data is obtained that includes measured signal strengths, such as RSSI data, at known locations, such as at known distances from a transmitter. According to some implementations, the training set of data is gathered by a mobile device having a GPS receiver, where the mobile device logs respective transmitter signal strengths at various locations (e.g., thousands of locations) near one or more towers having differing geometries (e.g., height, orientation, etc.) The training set can be gathered once. According to some implementations the training data can be used to generate parameters for the statistical model, as described below, where the parameters are stored on each mobile device. According to some implementations, the training set of data can be stored by mobile devices or stored remotely at a server using a database. Signals for several hundred thousand data points can be collected and included in the training set. The mean and standard deviation functions can be estimated from the training data set of measured signal strengths at known locations for example, via a standard least-squares fitting algorithm.

FIG. 6B shows a second process 650 of determining the contribution to the statistical model 530 based on the measured power levels (e.g., signal strength) of signals received by the device from one or more transmitters 505 and the location of known transmitters 510. Pairs of sources from which a signal is received by the device are identified 605. According to some implementations, all possible pairs of towers for which the device receives signals are considered. For instance, if there are three towers A, B, and C, the pairs A,B, A,C, and B,C will be considered.

A term is added to the statistical model for pairs of sources 670 based on the identified location of each pair of sources 660 and the identified signal strength received from each source 665. The term added to the statistical model for each pair of sources reflects that a conditional probability that the mobile device is at a distance d from a point ‘p’ on a line joining the pair of the multiple transmitters follows a log-normal distribution having mean and standard deviations that are functions of a signal strength ratio between the two transmitters in the pair. The location of the point ‘p’, mean, and standard deviation are estimated from a training data set of measured signal strengths at known locations for example, via a standard least-squares regression.

It will be appreciated that although least-squares regression is described herein for the first and second processes 600, 650 of determining the contribution to the statistical model 530 based on the measured power levels (i.e., signal strength) of signals received by the device from one or more transmitters 505 and the location of known transmitters 510, other techniques including other regression techniques can be used to calculate the parameters of the statistical model.

C. Historical Position Information and/or Geographical Information Contribution to a Statistical Model

As described with respect to FIG. 5, historical position information 515 can optionally be used to generate and/or modify the statistical model 530. According to some implementations, a term can be added to the statistical model that reflects that a conditional probability that the mobile device is at a given location relative to the historical position(s) follows a radially symmetric Gaussian distribution about the previously known location, with standard deviation based on an accuracy estimate of the known location (if available), together with information on how recent the known location measurement was taken. For instance, recent measurements can be presumed to be more accurate than old measurements.

As was further described with respect to FIG. 5, geographical information 520 can be used to add an additional term to the statistical model that provides a bias to locations that the mobile device has a greater likelihood to be near.

D. Estimating Location Using a Statistical Model

According to some implementations, to compute the likelihood that the mobile device is at a given location given all of the terms in the statistical model, the logarithm of the unnormalized conditional probability of each term is computed for a given location. These logarithms are summed to give a log-likelihood for a given position. However, because the mobile device can be at any geographical position, the log-likelihood for given positions are only calculated for a set of positions that are in a region surrounding the last known position, or last estimated position, of the mobile device. This permits the position estimator 404 to limit the number of calculations required to estimate the location of the mobile device.

FIG. 7 shows a high level method 700 that can be performed to determine an estimated location of a mobile device using a statistical model. If historical position information is known 705, a region surrounding the last known position of the mobile device is identified 710. According to some implementations, the region can be a circular region surrounding the mobile device. An error estimate for the last known position of the mobile device can also be generated. Sample positions are then selected (i.e., drawn) at random or pseudo randomly from the identified region 715.

Alternatively, if no historical position information is available 705, the transmitter that exhibits the strongest measured signal strength at the mobile device is identified 720, and sample positions are then selected (i.e., drawn) at random or pseudo randomly from a region surrounding the transmitter that includes the transmitter 725. According to some implementations, the calculation of a region surrounding the last known position of the mobile device, or the region surrounding the transmitter exhibiting the strongest signal strength at the mobile device, can be made by the position estimator 404. Similarly, the position estimator 404 can select sample positions within the region.

After sample positions are selected, the probability values for each sample position are determined using the statistical model 730. According to some implementations, the probability values can be determined by the position estimator 404. As described with respect to FIGS. 5 and 6, the statistical model is based on the measured power levels (i.e., signal strength) of signals received by the device from one or more transmitters 505 and the location of known transmitters 510. The model is optionally also based on historical position information 515 and geographical information 520. The respective probability values for each sample position indicate a probability that the mobile device is in the corresponding position. These probability values, in turn, can be used to identify an estimated position of the mobile device.

According to some implementations, the sample position exhibiting the highest probability value is selected 735, and the estimated position is identified 745 as that sample position. According to some implementations, the estimated position 745 can be identified as the calculated centroid of the distribution of sample positions 740 based on the probability values of each sample position included in the random (or pseudo-random) selection

According to some implementations, an error estimate for the estimated position is identified 750, which can be a function of the log-likelihood having parameters based on a training corpus of known locations and signal measurements via least-squares regression. It will be appreciated that although least-squares regression is described herein that other techniques including other regression techniques can be used to calculate the error estimate.

In some situations the mobile device may fail to receive signal strengths from one or more known transmitters, and possibly all transmitters. When this occurs, the calculation and identification of the estimated position can be postponed for a period of time (e.g., 1 second, 5 seconds, 1 minute, or until a signal strength is measured). Once signal strength measurements are available, the estimated position of the mobile device can be identified based on the new signal strength measurements.

E. Example Log-Likelihood Computation of Sample Point

Using the process described above with respect to FIG. 7, one or more sample positions can be identified at random or pseudo randomly as within a region surrounding a last known position of the mobile device, or the region surrounding the transmitter exhibiting the strongest signal strength at the mobile device. Below is an example process for computing the log-likelihood for one sample position.

Using the first process 600 for computing the contribution of signal strength measurements to the log-likelihood of a sample position, each tower contributes to the total log-likelihood of the sample position:

${{tower\_ log}{\_ likelihood}} = {\frac{- \left( {{\log (d)} - {\mu (s)}} \right)^{2}}{2\; \sigma \; (s)^{2}} - {\log (d)}}$

where d is the distance between the source and the sample position, and s is the measured signal strength from the source (as calculated, for instance, from a corpus of training data.)

In the above equation μ(s) and σ(s) are linear functions of the form f(x)=a x+b, whose exact parameters (a, b) are estimated statistically from a corpus of training data. As described above, the training set of data includes signal strength measurements (in power) for GPS-provided distances from a transmitter. In some implementations, to estimate μ(s), the best linear fit for the log of the distance in terms of the measured power of the signal strength can be estimated where the parameters (a, b) can be selected to minimize the expression: sum_(training measurements)(log(exact distance between device and tower)−(a*measured power+b))², and the function μ (s) is equal to ax+b. In some implementations, to estimate σ(s), for each distinct power level that the mobile device can measure, a variance is computed as: variance(power)−square_root(sum_(measurements with that power level)(log(exact distance between device and tower)−μ(power))²). Parameters (c, d) can then be selected to minimize the expression: sum_(power levels)(variance(power)−(c*power+d))², and the function σ (x) is equal to cx+d.

Alternatively, using the second process 650 for computing the contribution of signal strength measurements to the log-likelihood of a sample position, each pair of sources having respective locations T1 and T2 and measured signal strengths s1 and s2 contribute to the total log-likelihood of the sample position. Where the sources are ordered such that s1>s2, and R is the ratio of s1/s2, the location of point ‘P’ on a line joining the pair of the multiple transmitters can be determined as:

$P = {{T\; 1} + {\frac{2R^{c}}{\left( {1 - R^{c}} \right)}\left( {{T\; 1} - {T\; 2}} \right)}}$

where c is a parameter whose value can be estimated statistically from a corpus of training data. If d is the distance between the sample position and point ‘P’, the source-pair's contribution to the total log-likelihood of the sample position is:

${{tower\_ log}{\_ likelihood}} = {\frac{- \left( {{\log (d)} - {\mu (R)}} \right)^{2}}{2\; \sigma \; (R)^{2}} - {\log (d)}}$

where μ(r) and σ(r) are linear functions of the form f(x)=ax+b, whose exact parameters (a, b) are estimated statistically from a corpus of training data as described above.

As described with respect to FIG. 5, historical position information can optionally contribute to the statistical model. In this example, history position information contributes to the likelihood of a sample point. A radius r for the expected location about the historically known location is computed based on the accuracy estimate of the old location and the time since that estimate was made. If the distance between a sample point and the historical location is d, the historical contribution to the log likelihood of the sample point is:

${{history\_ log}{\_ likelihood}} = \frac{- d^{2}}{r^{2}}$

Finally, to compute the total log-likelihood of a sample position, all of the contributing terms can be summed. Each of the above calculations can be implemented, for instance, by the position estimator 404. As described with respect to FIG. 7, the log-likelihoods for each sample position can be calculated in order to estimate the position of the mobile device.

FIG. 8 shows an illustrative map display 802 on an example mobile device 100. The map display 802 can display the estimated position 816 of the mobile device 100 on a map to enable a user of the device 100 to identify his or her location. The map can include one or more objects, such as buildings, streets, geographical features, and the like, as is known in the art.

The disclosed and other embodiments and the functional operations described in this specification can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. The disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer-readable medium for execution by, or to control the operation of, data processing apparatus. The computer-readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more them. The term “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them. A propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus.

A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub-programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. However, a computer need not have such devices. Computer-readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

To provide for interaction with a user, the disclosed embodiments can be implemented on a computer having a display device, e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input.

The disclosed embodiments can be implemented in a computing system that includes a back-end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front-end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of what is disclosed here, or any combination of one or more such back-end, middleware, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network (“LAN”) and a wide area network (“WAN”), e.g., the Internet.

The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.

While this specification contains many specifics, these should not be construed as limitations on the scope of what being claims or of what may be claimed, but rather as descriptions of features specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particular order, this should not be understand as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

Particular embodiments of the subject matter described in this specification have been described. Other embodiments are within the scope of the following claims. For example, the actions recited in the claims can be performed in a different order and still achieve desirable results. As one example, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain implementations, multitasking and parallel processing may be advantageous. 

1. A method comprising: obtaining power information indicating a detected power of respective signals received in a mobile device from multiple transmitters; determining, using at least the obtained power information, respective probability values for a plurality of positions, each probability value indicating a probability that the mobile device is in a corresponding position; and identifying an estimated position of the mobile device based at least in part on the determined probability values.
 2. The method of claim 1, wherein determining the probability values and identifying the estimated position comprise: generating a statistical model based at least in part on the obtained power information; selecting a geographical region to which the generated statistical model applies; and randomly or pseudo randomly selecting a plurality of positions within the selected geographical region, wherein each of the probability values is identified as being associated with a corresponding one of the plurality of positions.
 3. The method of claim 2, further comprising: determining that a previous location of the mobile device has been registered, wherein the geographical region is selected taking into account the registered previous location.
 4. The method of claim 2, further comprising: determining a first transmitter, among the multiple transmitters, having a strongest signal according to the obtained power information, wherein the geographical region is selected taking into account a location of the determined first transmitter.
 5. The method of claim 2, wherein multiple previous location determinations have been performed, the method further comprising: generating an error estimate for a most recent of the previous location determinations, wherein the geographical region is selected taking into account the generated error estimate.
 6. The method of claim 2, wherein the statistical model is configured to have at least one term added and be taken into account in determining the probability values.
 7. The method of claim 6, further comprising: for each of the multiple transmitters, adding a term to the statistical model, the term reflecting that a conditional probability that the mobile device is a distance d from the respective transmitter follows a log-normal distribution, wherein a mean and a standard deviation of the log-normal distribution are functions of the power of the respective transmitter.
 8. The method of claim 7, further comprising: obtaining a training data set comprising signal strength information regarding known locations; and estimating the functions for the mean and the standard deviation using the obtained training data set.
 9. The method of claim 6, further comprising: for each pair of the multiple transmitters, adding a term to the statistical model, the term reflecting that a conditional probability that the mobile device is at a distance d from a point on a line joining the pair of the multiple transmitters follows a log-normal distribution, wherein a mean and a standard deviation are functions of the powers of the respective two transmitters.
 10. The method of claim 9, further comprising: obtaining a training data set comprising signal strength information regarding known locations; and estimating the functions for the mean and the standard deviation using the obtained training data set.
 11. The method of claim 6, further comprising: obtaining a previously estimated location for the mobile device; and adding a term to the statistical model, the term reflecting that a conditional probability that the mobile device is at a distance d from the previously estimated location follows a radially symmetric Gaussian distribution about the previously estimated location.
 12. The method of claim 11, wherein a standard deviation of the radially symmetric Gaussian distribution is based on an error estimate and on information about how recently the previously estimated location was identified.
 13. The method of claim 6, further comprising: obtaining geographical information relating to at least one of the plurality of positions; and adding a term to the statistical model based on the obtained geographical information.
 14. The method of claim 13, wherein the geographical information provides a bias toward some locations over other locations.
 15. The method of claim 1, wherein identifying the estimated position comprises: selecting one of the determined probability values that is associated with a highest probability that the mobile device is in the corresponding position.
 16. The method of claim 1, wherein identifying the estimated position comprises: determining a centroid location based on the determined probability values; and selecting the determined centroid location as the estimated position.
 17. The method of claim 1, further comprising: determining that additional power information is required to identify the estimated position; postponing the identification of the estimated position for a period of time; and collecting the additional power information, wherein the estimated position of the mobile device is identified based also on the additional power information.
 18. A computer program product, encoded on a tangible program carrier, operable to cause a portable device to perform operations comprising: obtaining power information indicating a detected power of respective signals received in a mobile device from multiple transmitters; determining, using at least the obtained power information, respective probability values for a plurality of positions, each probability value indicating a probability that the mobile device is in the corresponding position; and identifying an estimated position of the mobile device based at least in part on the determined probability values.
 19. A mobile device comprising: a processor-accessible medium containing power information that indicates a detected power of respective signals received in a mobile device from multiple transmitters; and a position estimator that 1) determines, using at least the obtained power information, respective probability values for a plurality of positions, each probability value indicating a probability that the mobile device is in the corresponding position; and 2) identifies an estimated position of the mobile device based at least in part on the determined probability values. 